Coaxial motorcycle

ABSTRACT

In a coaxial two-wheeled vehicle, an attitude controller ( 84 ) calculates motor torque Tgyr for maintaining a base so that it has a target angle from deviation between base angle command θref serving as attitude command and current base angle θ 0  calculated by using a gyro sensor ( 13 ) and an acceleration sensor ( 14 ). On the other hand, at a position proportional controller ( 86 R), a differentiator ( 88 R) and a velocity proportional controller ( 89 R), there is performed PD control with respect to deviation between rotation position command Prefr of a motor rotor ( 92 R) for right wheel and current rotation position θr of a motor rotor ( 92 R). A current control amplifier ( 91 R) generates motor current on the basis of added value of motor torque which is the control result and estimated load torque T 1  calculated by using pressure sensors to drive the motor rotor ( 92 R).

TECHNICAL FIELD

The present invention relates to a coaxial two-wheeled vehiclecomprising wheels at both ends of the same axle.

This Application claims priority of Japanese Patent Application No.2003-168224, and Japanese Patent Application No. 2003-168226, which arefiled on Jun. 12, 2003, the entireties of which are incorporated byreference herein.

BACKGROUND ART

Studies of coaxial two-wheeled vehicles comprising wheels at the samewheel axle (shaft) have been conventionally developed because thesecoaxial two-wheeled vehicles are advantageous from viewpoint ofrealization of compact configuration in plane shape even as compared tonot only four-wheeled vehicle or three-wheeled vehicle, but alsodifferent axial two-wheeled vehicle in which rotation shafts (axles) ofindividual wheels are different like bicycle. However, as long as theproblem of stable control of attitude cannot be overcome even in suchcoaxial two-wheeled vehicle, putting into practice thereof isimpossible.

From reasons as described above, as a technique of performing stablecontrol of attitude, e.g., in the Japanese Patent Application Laid OpenNo. 1988-305082 publication, there is proposed a technology to perform,at short time interval, sampling of inclination (tilt) angles of vehiclebody detected by rotary encoder, etc. to calculate control torques ofmotors for driving wheels on the basis of sampled values, and toinstruct the wheel drive motors to perform operations corresponding tothe control torques to thereby immediately move, when the vehicle bodyis inclined, wheels in inclination direction thereof to performrestoration of the vehicle body.

Moreover, in the U.S. Pat. No. 5,871,091 specification, there isproposed a technology to detect inclination (tilt) angle of a vehiclebody by plural gyro sensors to perform feedback of the state of thecontrol unit of the motors so that these gyro sensor signals are causedto be horizontal to thereby travel in the state where the vehicle bodyis maintained to be horizontal.

However, in such coaxial two-wheeled vehicles described in the JapanesePatent Application Laid Open No. 1988-305082 publication and the U.S.Pat. No. 5,871,091 specification, in the case where the human being isridden, or in the case where the human beings having large weightdifference are alternatively ridden, inertia moment and/or load weightwhen viewed from the motor are changed to much degree so that thecontrol system for stabilizing the attribute becomes unstable. For thisreason, there were problems that extraordinary vibration may take placewhen the human being rides or alights, and/or the operation may bechanged by difference between weights of human beings.

Further, there is the problem that the vehicle body may be advanced orreversed by slight movement of center of gravity that a person who rideson the vehicle (hereinafter simply referred to as rider) does notintend. In addition, when position of center of gravity is moved greatlytoward forward or backward direction, there was the possibility that thevehicle velocity is excessively increased so that it may fall down.

DISCLOSURE OF THE INVENTION

The present invention has been proposed in view of such conventionalactual circumstances, and its object is to provide a coaxial two-wheeledvehicle which is stable with respect to change in load weight, and whichcan stably and compatibly realize attitude control and travelingcontrol.

Another object of the present invention is to provide a coaxialtwo-wheeled vehicle which can travel in safety and stably even ifposition of center of gravity of rider is moved.

To attain the above-described objects, the coaxial two-wheeled vehicleaccording to the present invention is directed to a coaxial two-wheeledvehicle comprising a pair of wheels, a wheel axle installed or providedbetween the pair of wheels, a base supported on the wheel axle so thatit can be inclined thereon, a pair of drive motors for driving the pairof respective wheels, and a control unit for sending an operationcommand to the pair of drive motors, wherein load detecting means fordetecting position and weight on the base and angle detecting means fordetecting angle about the wheel axle of the base are provided on thebase, and the control unit is composed of a first control mechanismadapted to generate a first torque for canceling torque based on theload and a second torque for maintaining the base so that it has apredetermined angle in correspondence with angle about the wheel axle ofthe base, and a second control mechanism independent of the firstcontrol mechanism, which is adapted to generate a third torque forperforming traveling operation in accordance with position of the load,thus to instruct the pair of drive motors to perform operationscorresponding to the first to third torques.

In such coaxial two-wheeled vehicle, there are produced first torque forcanceling torque based on load on the base, which has been detected byload detecting means comprised of, e.g., plural pressure sensors, secondtorque for maintaining the base so that it has a predetermined angle incorrespondence with angle about the wheel axle of the base, which hasbeen detected by angle detecting means composed of, e.g., gyro sensorand acceleration sensor, and third torque for performing travelingoperation in accordance with the position of the load, thus to instructpair of respective drive motors to perform operations corresponding tothe first to third torques to drive the pair of wheels.

Moreover, in order to attain the above-described objects, the coaxialtwo-wheeled vehicle according to the present invention is directed to acoaxial two-wheeled vehicle comprising a pair of wheels, a wheel axleinstalled or provided between the pair of wheels, a base supported onthe wheel axle so that it can be inclined thereon, a pair of drivemotors attached on the base and for driving the pair of respectivewheels, and a control unit for sending an operation command to the pairof drive motors, wherein load detecting means for detecting position andweight of load on the base is provided on the base, and the control unitis operative so that in the case where position of the load is within apredetermined stop region, it does not a traveling command, while in thecase where position of the load is not within the stop region, it sendsa traveling command corresponding to that position to the pair ofrespective drive motors.

In such coaxial two-wheeled vehicle, in the case where the position ofload on the base is within a predetermined stop region, e.g., the rangein a direction perpendicular to the wheel axle is inside of the range ina direction perpendicular to the wheel axle of ground-contacting regionwhere the pair of wheels are in contact with the road surface, it doesnot send the traveling command, while in the case where such position isnot within the stop region, it sends traveling command corresponding tothat position.

Further, in order to attain the above-described objects, the coaxialtwo-wheeled vehicle according to the present invention is directed to acoaxial two-wheeled vehicle comprising a pair of wheels, a wheel axleinstalled or provided between the pair of wheels, a base supported onthe wheel axle so that it can be inclined thereon, a pair of drivemotors attached on the base and for driving the pair of respectivewheels, and a control unit for sending an operation command to the pairof drive motors, wherein load detecting means for detecting position andweight of load is provided on the base, and the control unit isoperative so that in the case where position of the load is within apredetermined deceleration region, it sends a traveling instruction toperform deceleration/stop operation to the pair of respective drivemotors, while in the case where position of the load is not within thedeceleration region, it sends a traveling command corresponding to thatposition to the pair of respective drive motors.

In such coaxial two-wheeled vehicle, in the case where position of loadon the base is within a predetermined deceleration region, e.g., withinthe region in the vicinity of the boundary of load detectable range bythe load detecting means, traveling instruction to performdeceleration/stop operation is sent, while in the case where suchposition is not within the deceleration region, it sends travelingcommand corresponding to that position.

Still further objects of the present invention and practical meritsobtained by the present invention will become more apparent from thedescription of the embodiments which will be given below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an outer appearance perspective view showing a coaxialtwo-wheeled vehicle in this embodiment.

FIG. 2 is a side cross sectional view for explaining base of the coaxialtwo-wheeled vehicle.

FIGS. 3A and 3B are views showing pressure sensor provided at the baseof the coaxial two-wheeled vehicle, wherein FIG. 3A shows a plan viewand FIG. 3B shows a side view.

FIG. 4 is a view showing positional relationship between center ofweight and wheel axle of the coaxial two-wheeled vehicle.

FIG. 5 is a view for explaining balance between load torque and motortorque.

FIG. 6 is a view for explaining attitude control in the case where thehuman being is ridden.

FIG. 7 is a view for explaining dynamical model for maintaining attitudeon base.

FIG. 8 is a view for explaining dynamical model for maintaining attitudeon the base.

FIG. 9 is a view for explaining dynamical model for maintaining attitudeon the base.

FIG. 10 is a view for explaining dynamical model in the coaxialtwo-wheeled vehicle.

FIG. 11 is a view showing a control mechanism for attitude stabilizationcontrol.

FIG. 12 is a view showing a control mechanism for attitude stabilizationcontrol and traveling control in the case where a single wheel isprovided.

FIG. 13 is a view for explaining attitude command in the coaxialtwo-wheeled vehicle.

FIG. 14 is a block diagram showing control mechanism for attitudestabilization control and traveling control in the case where a singlewheel is provided.

FIG. 15 is a view showing the block diagram shown in FIG. 14 asmathematical model.

FIG. 16 is a view showing a detailed practical example of themathematical model shown in FIG. 15.

FIG. 17 is a block diagram showing control mechanism for attitudestabilization control and traveling control in the case where two wheelsare provided.

FIG. 18 is a view for explaining traveling velocity control in the casewhere forwarding/reversing operation is performed.

FIG. 19 is a view for explaining traveling velocity control in the caseof performing swivel operation.

FIG. 20 is a view for explaining a control method in the case where gyrosensor signal about yaw axis is detected in performing straightforwarding operation.

FIGS. 21A and 21B are views for explaining a velocity control method inthe case where acceleration signal in Z-axis direction is detected,wherein FIG. 21A is a view showing the state where vehicle body rides onoffset, and FIG. 21B is a view showing changes of traveling velocity andZ-axis acceleration.

FIGS. 22A and 22B are views for explaining image recognition processingin the coaxial two-wheeled vehicle, wherein FIG. 22A is a view showingCCD camera provided on the base, and FIG. 22B is a view showing thestate of obstacle detection by the CCD camera.

FIGS. 23A and 23B are views for explaining sound (speech) recognitionprocessing in the coaxial two-wheeled vehicle, wherein FIG. 23A is aview showing microphone provided on the base, and FIG. 23B is a viewshowing the state of sound source detection by the microphone.

FIG. 24 is a block diagram showing control mechanism which realizessound source detection during traveling operation, etc.

FIG. 25 is a view for explaining software configuration of the coaxialtwo-wheeled vehicle.

FIG. 26 is a view for explaining the entire configuration of respectivecircuits of the coaxial two-wheeled vehicle 1.

FIGS. 27A and 27B are views for explaining detailed internalconfiguration of the entire configuration shown in FIG. 26.

BEST MODE FOR CARRYING OUT THE INVENTION

Practical embodiments to which the present invention is applied will nowbe described in detail with reference to the attached drawings. In thisembodiment, the present invention is applied to a coaxial two-wheeledvehicle comprising wheels at both ends of the same axle (shaft).

Initially, outer appearance view of the coaxial two-wheeled vehicle inthis embodiment is shown in FIG. 1. In the coaxial two-wheeled vehicle 1shown in FIG. 1, a pair of wheels 3 (right wheel 3R and left wheel 3L)are fixedly attached at both ends of a wheel axle 2. The wheel 3 isformed by rubber material having elastic characteristic, wherein air ornitrogen gas, etc. is filled within the wheel 3. By adjusting gaspressure to adjust elasticity of the wheel 3, vibration of the vehiclebody is absorbed, thereby making it possible to reduce vibration byuneven portions of the road surface and/or impact by offset. Moreover,although not shown, grooves having uneven shape are formed at thesurface of the wheel 3. Thus, it is possible to maintain high frictionforce at the time of traveling operation on uneven road surface, and/orriding over an offset.

Moreover, at the wheel axle 2, e.g., a base 4 on which substantiallyparallelepiped case where control unit, etc. which will be describedlater is accommodated below plate-shaped body adapted so that, e.g., thehuman being is ridden in the standing attitude is supported so that itcan be inclined about the wheel axle 2. On the base 4, there is provideda handle 5 adapted to be grasped by both hands when, e.g., the humanbeing is ridden.

Hereinafter, in this specification, the intermediate point of the wheelaxle 2 connecting the both wheels is assumed as origin O of the X-Y-Zcoordinate system, and the direction passing though the origin O and inparallel to the principal surface of the base 4 and perpendicular to thewheel axle 2 is defined as X-axis or roll axis, and wheel axle (shaft)direction passing through the origin O is defined as Y-axis or pitchaxis, and the direction passing through the origin O and perpendicularto the principal surface of the base 4 is defined as yaw axis. Inaddition, the forward direction of the coaxial two-wheeled vehicle 1 isdefined as positive direction of the X-axis, the left direction thereofis defined as positive direction of the Y-axis, and the upper directionof the Z-axis is defined as positive direction of the Z-axis.

As shown in FIG. 2, reversible motors (10R and 10L) are attached on thebase 4. Rotary encoders 11 (11R and 11L) for detecting rotationalposition of the motor 10 are provided in a manner adjacent to the motor10. Moreover, decelerators 12 (12R and 12L) comprised of toothed wheelor timing belt are caused to intervene between the motor 10 and thewheel 3. Thus, rotation of the motor 10 is transmitted to the wheel 3through the decelerators 12 and joints (not shown).

The decelerator 12 has backlash quantity of one minute or less, and hasthe characteristic (back drivability characteristic) in which whenrotational torque is applied by external force from the output shaft ofthe wheel 3 side, rotation torque is transmitted also to the input shaftof the motor 10 side so that the motor 10 is easily rotated. By usingsuch decelerator 12 having back-drivability characteristic, when landingdown from, e.g., air state, the motor 10 absorbs reactive force of theroad surface so that it is attenuated. Thus, landing can be stablyperformed. Moreover, even in the case where power supply is interrupted,external force is applied to the vehicle body to rotate the motor 10,thus making it possible to easily move the vehicle body. Further, in thecase where the vehicle body descends in accordance with gravity ofslope, rotation torque is transmitted to the motor 10 so that counterelectromotive force takes place. However, charging operation of battery(not shown) is performed by making use of this counter electromotiveforce, thus making it possible to elongate battery drive time. It is tobe noted that in the case where the battery is completely charged, acontrol to discharge regenerative power as heat by regenerativeresistance is performed. In addition, there is included power supplymanagement circuit (which will be described later) such that not onlyregenerative power produced at down slope, but also regenerative powerat the time of deceleration are charged into the battery.

Further, at the base 4, there are included, in addition to gyro sensor13 for detecting pitch axis, and angular velocities ωp, ωyaw of the base4, various sensors such as acceleration sensors 14 for detecting linearaccelerations Ax, Ay, Az in X, Y, Z axis directions, and angularaccelerations αp, αr, αyaw about the pitch axis, the roll axis and theyaw axis, and a pressure sensor 15 for detecting load weight on the base4, etc.

Among them, as shown in the plan view of FIG. 3A and the side view ofFIG. 3B, the pressure sensors 15 are provided at four corners betweensupporting table 4 a and movable table 4 b which constitute plate-shapedbody of the base 4, thus making it possible to detect gravity centercoordinate (X_(g), Y_(g)) of load on the base 4 and its load weightW_(g) from sensor signals of the four pressure sensors 15 ₁ to 15 ₄.Namely, in the case where sensor signals of the pressure sensors 15 ₁ to15 ₄ are respectively PS₁, PS₂, PS₃, PS₄, and self-weights applied tothe pressure sensors 15 ₁ to 15 ₄ in no-load state are W₀, load weightWg is calculated by the following formula.W _(g)=PS₁+PS₂+PS₃+PS₄ −W ₀  (1)

Moreover, in the case where X-coordinates of the pressure sensors 15 ₁,15 ₄ and the pressure sensors 15 ₂, 15 ₃ are respectively Xps, −Xps, andY-coordinates of the pressure sensors 15 ₁, 15 ₂ and the pressuresensors 15 ₃, 15 ₄ are respectively Yps, −Yps, gravity coordinate(X_(g), Y_(g)) is determined by the following formula (2). Here, in theformula (2), W₁₄ indicates self-weight applied to the pressure sensors15 ₁, 15 ₄ in no-load state, W₂₃ indicates self-weight applied to thepressure sensors 15 ₂, 15 ₃ in no-load state, W₁₂ indicates self-weightapplied to the pressure sensors 15 ₁, 15 ₂ in no-load state, and W₃₄indicates self-weight applied to the pressure sensors 15 ₃, 15 ₄ inno-load state.

$\left\{ \begin{matrix}{X_{g} = {X_{PS}*{\left( {{W\; 1} - {W\; 2}} \right)/\left( {{W\; 1} + {W\; 2}} \right)}}} \\{Y_{g} = {Y_{PS}*{\left( {{W\; 3} - {W\; 4}} \right)/\left( {{W\; 3} + {W\; 4}} \right)}}}\end{matrix}\quad \right.$where

$\begin{matrix}\left\{ \begin{matrix}{{W\; 1} = {{\left( {{PS}_{1} + {PS}_{4}} \right)/2} - W_{14}}} \\{{W\; 2} = {{\left( {{PS}_{2} + {PS}_{3}} \right)/2} - W_{23}}} \\{{W\; 3} = {{\left( {{PS}_{1} + {PS}_{2}} \right)/2} - W_{12}}} \\{{W\; 4} = {{\left( {{PS}_{3} + {PS}_{4}} \right)/2} - W_{34}}}\end{matrix}\quad \right. & (2)\end{matrix}$

Since load torque T₁ based on load on the base 4 is calculated by thepressure sensor 15, moment of reaction is given to the motor 10, therebymaking it possible to maintain balance on the base 4 to stabilizeattitude.

Furthermore, a control unit 16 comprised of microcomputer is mounted atthe lower case of the base 4, and various sensor signals and detectionsignals are inputted to the control unit 16. The control unit 16controls the vehicle body so as to produce motor torque serving toadvance, reverse or swivel the vehicle body while maintaining pitch axisangle and yaw axis angle of the base 4 at suitable values as describedlater.

In addition, as shown in FIG. 4, the coaxial two-wheeled vehicle 1 iscaused to be of the configuration in which weight center M of the base 4(and the handle 5) which can be inclined about the wheel axle (shaft) 2is positioned below the wheel axle 2. Thus, also at the time of stop,the vehicle body is maintained so that gravity position is located atthe most stable position, and is difficult to fall down. It is to benoted that while the height of the upper surface of the base 4 is higherthan the wheel axle 2 in FIG. 4, the upper surface of the base 4 may belower than the wheel axle 2.

Here, the control concept for maintaining the attitude on the base 4will be explained. As shown in FIG. 5, when motor torque Tm iscontrolled so that the same moment is produced with respect to loadtorque T₁ based on load on the base 4, e.g., load torque T₁ by, e.g.,weight of the human being, balance of the base 4 is maintained withfulcrum being as center like seesaw. The point corresponding to fulcrumwhich maintains the balance, i.e., the point where rotational momentabout the wheel axle 2 becomes equal to zero is called ZMP (Zero MomentPoint). When the ZMP coincides with ground contacting point with respectto the road surface of the wheel 3, or is located within the groundcontacting surface with respect to the road surface, the balance iskept, thus making it possible to maintain the attitude on the base 4.

When the human being having weight Wh is ridden on the coaxialtwo-wheeled vehicle 1, weight center M of the base 4 and the handle 5 isinclined with the wheel axle 2 being as center in accordance withinclination angle θ of the human being. At this time, the wheel axletorque T₀ that the wheel axle 2 takes balance is represented by thefollowing formula (3), and motor torque Tm for maintaining attitude isrepresented as T₀/N when deceleration ratio of the decelerator 12 isexpressed as N:1.T ₀ =Wh*sin θ−Wm*sin θ  (3)

In the coaxial two-wheeled vehicle 1 in this embodiment, since weightcenter M of the base 4 and the handle 5 is constituted as describedabove so that it is positioned below the wheel axle 2, it is sufficientto only add, as wheel axle torque T₀, difference between moment based onweight Wh of the human being and moment based on weight Wm of the base 4and the handle 5. Thus, it is possible to maintain balance by relativelysmall motor torque.

The dynamical model for maintaining the attitude on the base 4 will beexplained in more detail by using the X-Z coordinate system shown inFIG. 7. Here, in FIG. 7, for the brevity, explanation will be given onthe premise that single wheel 3 is provided. Moreover, the wheel 3, thebase 4 and the human being on the base 4 are respectively regarded aslinks, and their gravity position coordinates are respectively expressedas (x₀, z₀), (x₁, z₁) and (x₂, z₂). Further, masses of the respectivelinks are respectively expressed as m₀, m₁, m₂, and inertia moments arerespectively as I₀, I₁, I₂.

When gravity center position coordinate is expressed as (x_(i), z_(i)),respective momentums of the i-th link (i=0, 1, 2) about the definedpoint Ω(σ, φ) are represented by the following formula (4). Here, in theformula (4), respective single dots attached over x, z indicate firstorder differentiation of x, z.Ii*ωi+mi*{dot over (x)}i(φ−zi)−mi*żi(σ−xi)  (4)

Accordingly, moment by inertia force of all links is represented by thefollowing formula (5). Here, respective two dots attached over x, z inthe formula (5) indicate second order differentiation of x, z. Inaddition, when gravity acceleration is g, moment by gravity of all linksis represented by the following formula (6).

$\begin{matrix}{\sum\limits_{i = 0}^{n}\left( {{{Ii}*\overset{.}{\omega}i} + {m\; i*{\overset{¨}{xi}\left( {\phi - {zi}} \right)}} - {m\; i*{\overset{¨}{zi}\left( {\sigma - {xi}} \right)}}} \right)} & (5) \\{\sum\limits_{i = 0}^{n}{m\;{i\left( {\sigma - {xi}} \right)}g}} & (6)\end{matrix}$

By sum of moment by this inertia force and moment by gravity, moment MΩabout the point Ω(σ, φ) is given as shown in the following formula (7).

$\begin{matrix}\begin{matrix}{{M\;\Omega} = {{\sum\limits_{i = 0}^{n}{{Ii}*\overset{.}{\omega}\; i}} + {\sum\limits_{i = 0}^{n}{m\; i\text{(}{\overset{¨}{xi}\left( {\phi - {zi}} \right)}}} - {\overset{¨}{zi}\left( {\sigma - {xi}} \right)} +}} \\{\sum\limits_{i = 0}^{n}{m\;{i\left( {\sigma - {xi}} \right)}g}}\end{matrix} & (7)\end{matrix}$

If moment by gravity of wheel 3 which is mass m₀ is excluded, point Ω(σ,φ) is taken as origin so that the above-described moment MΩ results inmoment Ma about the wheel axle 2. The moment Ma about the wheel axle 2is represented by the following formula (8),

$\begin{matrix}{{Ma} = {{\sum\limits_{i = 0}^{n}{{Ii}*\overset{.}{\omega}\; i}} + {\sum\limits_{i = 0}^{n}{m\;{i\left( {{\overset{¨}{zi}*{xi}} - {\overset{¨}{xi}*{zi}}} \right)}}} - {\sum\limits_{i = 0}^{n}{m\; i*{xi}*g}}}} & (8)\end{matrix}$

If the above-described moment MΩ is represented by using this moment Ma,when x₀=0, i.e., gravity center position of the wheel 3 exists on thewheel axle 2, the moment MΩ is given by the following formula (9).

$\begin{matrix}{{M\;\Omega} = {{Ma} - {\sum\limits_{i = 0}^{n}{m\;{i\left( {\overset{¨}{zi} - g} \right)}\sigma}} + {\sum\limits_{i = 0}^{n}{m\; i*\overset{¨}{xi}*\phi}}}} & (9)\end{matrix}$

Here, ZMP is defined as point on the floor surface where moment MΩ is 0(zero). In view of the above, height of the wheel axle 2 is expressed ash and coordinate of ZMP is expressed as (σzmp, −h) to substitute thesevalues into the formula (7), the following formula (10) is provided. Bysolving this formula (10) with respect to σzmp, it is possible torepresent ZMP by link position, acceleration and mass.

$\begin{matrix}\begin{matrix}{0 = {{\sum\limits_{i = 0}^{n}{{Ii}*\overset{.}{\omega}\; i}} + {\sum\limits_{i = 0}^{n}{m\;{i\left( {{- {\overset{¨}{xi}\left( {h + {zi}} \right)}} - {\overset{¨}{zi}\left( {{\sigma\;{zmp}} - {xi}} \right)}} \right)}}} +}} \\{\sum\limits_{i = 0}^{n}{m\;{i\left( {{\sigma\;{zmp}} - {xi}} \right)}g}}\end{matrix} & (10)\end{matrix}$

Moreover, when coordinate (σzmp, −h) of ZMP is substituted into theabove-described formula (9), the following formula (11) is provided. Inthis case, the formula (11) indicates the formula of balance of momentabout the wheel axle 2.

$\begin{matrix}{0 = {{Ma} - {\sum\limits_{i = 0}^{n}{m\;{i\left( {\overset{¨}{zi} - g} \right)}\sigma\;{zmp}}} - {\sum\limits_{i = 0}^{n}{m\; i*\overset{¨}{xi}*h}}}} & (11)\end{matrix}$

Here, force exerted on ZMP is shown in FIG. 8. In FIG. 8, FN indicatesfloor reactive force, FT indicates rolling friction force, and Findicates resultant vector of FN and FT. It is to be noted that whilefloor reactive forces N are distributed in practice over the entirety ofground contacting surface of the wheel 3, those forces are intensivelyconcentrated into ZMP. When the formula of balance of moment about thewheel axle 2 is represented from this figure, the following formula (12)is provided.FN*σzmp+FT*h+τ0=0  (12)

In this case, when the following formulas (13) to (15) are substitutedinto the formula (12), the formula which is the same as theabove-described formula (11) is provided.

$\begin{matrix}{T_{0} = {Ma}} & (13) \\{{FN} = {- {\sum\limits_{i = 0}^{n}{m\;{i\left( {\overset{¨}{zi} - g} \right)}}}}} & (14) \\{{FT} = {- {\sum\limits_{i = 0}^{n}{m\; i*\overset{¨}{xi}}}}} & (15)\end{matrix}$

In order that attitude on the base 4 is stabilized, it is sufficientthat σzmp=0 in the formula (12). Namely, if wheel axle torque T₀=−FT*hholds, it is possible to maintain the attitude. Accordingly, bycontrolling state variable shown in the following formula (16) whichsatisfies T₀=FT=0, it is possible to stabilize the attitude.

$\begin{matrix}{\left( {{xi},{\overset{.}{x}i},\overset{¨}{xi}} \right) = \left( {0,0,0} \right)} & (16)\end{matrix}$

At this time, x₀, x₁ are univocally determined by the mechanicalstructure, but m₂, I₂, x₂, z₂ are infinite values because of the humanbeing. Moment Mt on the base 4 by m₂, I₂, x₂, z₂ is given by thefollowing formula (17). It is to be noted that the base is assumed to bekept horizontal as shown in FIG. 9.Mt=I ₂*{dot over (ω)}₂ +m ₂ *{umlaut over (z)} ₂ *x ₂ −m ₂ *{umlaut over(x)} ₂*(z ₂ −L)−m ₂ *x ₂ *g  (17)

Here, in the case where load is human being, since angular velocity ω₂is sufficiently small, when approximation into ω2≈0 is made, moment Mtbecomes equal to zero when x₂ and the second-order differential valueare caused to be zero in the formula (18). It can be considered thatallowing x₂ and the second-order differential value thereof to be equalto zero is equivalent to the fact that control of x₀ and x₁ is made sothat load torque T₁ on the base 4 becomes equal to zero. Moreover, themoment Mt by the load torque T₁ is equivalent to the fact that force F₂is exerted on working point (x_(f), L) on the base 4. Accordingly, ifz₀, x₁ which allow the x_(f) to be equal to zero can be given, T₁becomes equal to 0 (zero). Thus, it is possible to satisfy the conditionwhich stably maintains the attitude.

As shown in FIG. 9, when feedback control of a gyro sensor signal on thebase 4 is performed to give motor torque Tm so that control is made inorder to maintain x₀=x₁, motor torque Tm is controlled so that thereresults x_(f)=x₀, thereby making it possible to stably maintain theattitude.

In concrete terms, when error is expressed as E_(f)=x_(f)−x₀, ifE_(f)>0, the motor torque Tm is caused to be negative for the purpose ofperforming displacement of x₀ in a positive direction to advance thevehicle body. If E_(f)<0, motor torque Tm is caused to be positive forthe purpose of performing displacement of x₀ in a negative direction toreverse (withdraw) the vehicle body, thereby making it possible toconverge error E_(f) into zero. Namely, A₀ is caused to be positiveconstant to give motor torque Tm such that Tm=−A₀*E_(f) to therebyconverge E_(f) into zero, thereby making it possible to suitablymaintain the attitude.

In practice, e.g., in the case where the base 4 is inclined by angle θ₀about the pitch axis as shown in FIG. 10, since load torque of T₁(=Mτ×L)is produced by the human being having weight W, motor torque Tm iscontrolled in order to provide load torque T₁ and wheel shaft torque T₀in a direction opposite to the above to thereby allow ZMP to be incorrespondence with ground-contacting point of the wheel 3 to haveability to stably maintain the attitude.

Here, in the case where the human being is ridden on the base 4, sinceforce exerted on the back of the foot is changed in order to maintainthe attitude ordinarily at period of 1 to 2 seconds although individualdifference exists, load torque T₁ based on weight of the human being ischanged in indefinite manner. Accordingly, it is required to add atorque such that balance can be taken on the real time basis to themotor 10 to keep constant angle of the base 4 with respect to loadchange.

In view of the above, in order to cancel such load change on the realtime basis, the coaxial two-wheeled vehicle 1 in this embodiment has acontrol mechanism as shown in FIG. 11 within the control unit 16. InFIG. 11, at the subtracter 20, deviation between base angle command θrefserving as attitude command and current base angle θ₀ detected by thegyro sensor 13 and the acceleration sensor is taken. The deviation thusobtained is delivered to an attitude controller 21. The attitudecontroller 21 calculates motor torque current valve Tgyr[A] from thebase angle command θref and current base angle θ₀. Moreover, an adjuster22 serves to estimate load torque T₁ by using sensor signals PS₁, PS₂,PS₃, PS₄ of the pressure sensors 15 to calculate estimated load torquecurrent value T₁′/Km[A] for canceling the load torque T₁. Here, Km ismotor constant [Nm/A]. In the case where gravity center coordinate ofload is (X_(g), Y_(g)), and load weight is W_(g), estimated load torqueT₁′ is given by the following formula (18).T ₁ ′=W _(g) *X _(g)/2  (18)

Further, at a subtracter 23, deviation between motor torque currentvalue Tgyr and estimated load torque current value T₁′/Km is taken. Thedeviation thus obtained is delivered to a motor 24 as motor currentI[A]. The motor 24 is rotated by the motor current I. Thus, motor torqueTm is produced. At an adder 25, the motor torque Tm and load torque T₁are added. The added torque thus obtained is transmitted to a base 26.

As stated above, motor torque Tm for canceling load torque T₁ is addedto the motor 24, thereby making it possible to keep constant base anglewith respect to load change at the time of stop.

While attitude stabilization control can be performed by theabove-mentioned control mechanism, it is required for performingtraveling operation in this state to further provide control mechanismfor traveling control. In view of the above, the coaxial two-wheeledvehicle 1 in this embodiment has control mechanism of the doublestructure to independently determine, in practice, motor torque forattitude stabilization control and motor torque for traveling control.

The physical model of such control mechanism of the double structure isshown in FIG. 12. It is to be noted that, also in FIG. 12, for thebrevity, explanation will be given on the premise that single wheel 3 isprovided. As shown in FIG. 12, various sensors such as gyro sensor 13,acceleration sensor 14 and/or pressure sensor 15, etc. are includedwithin the base 4. A motor stator 30, a rotary encoder 31, and a motorrotor 32 exist at the lower portion thereof. Thus, rotation of the motorrotor 32 is transmitted to the wheel 3 through a decelerator 33 and ajoint 34.

An attitude controller/adjuster 40 calculates motor torque Tgyr andestimated load torque T₁′ which have been described above from baseangle command θref serving as attitude command, current base angle θ₀detected by the gyro sensor 13 and the acceleration sensor 14, andsensor signals PS₁, PS₂, PS₃, PS₄ of the pressure sensors 15. Moreover,a motor controller 41 calculates motor torque for traveling operationfrom rotational position command Pref of the motor rotor 32 serving astraveling command and current rotation position θr of the motor rotor 32detected by the rotary encoder 31.

Further, at an adder 42, motor torque Tgyr, estimated load torque T₁′and motor torque for traveling operation are added. The added value thusobtained is delivered to the motor rotor 32.

Here, the above-described base angle command θref is target value ofbase angle which is set in accordance with acceleration Ax in the X-axisdirection so that the rider can stably ride. In concrete terms, whenX-axis acceleration Ax is zero, setting is made such that the base 4 isplaced in horizontal direction, when X-axis acceleration Ax is positive,setting is made such that the base 4 is inclined in forward direction,and when X-axis acceleration Ax is negative, setting is made such thatthe base 4 is inclined in backward direction. For example, in the casewhere the X-axis acceleration Ax is positive, when the base 4 isinclined so that ZMP is positioned in a direction of resultant vector ofinertia force and gravity, the rider can stably maintain the attitude.In this example, the base angle command θref changes in a mannerproportional to the X-axis acceleration Ax.

The block diagram of the control mechanism is shown in FIG. 14. At asubtracter 50, deviation between base angle command θref serving asattitude command and current base angle θ₀ detected by the gyro sensor13 (and the acceleration sensor 14) is taken. The deviation thusobtained is delivered to an attitude controller 51. The attitudecontroller 51 calculates motor torque Tgyr from the base angle commandθref and current base angle θ₀ to deliver the motor torque Tgyr thuscalculated to an adder 54.

On the other hand, at a subtracter 52, deviation between rotationalposition command Pref of a motor rotor 57 serving as traveling commandand current rotational position θr of the motor rotor 57 detected by arotary encoder 58 is taken. The deviation thus obtained is delivered toa motor controller 53. The motor controller 53 calculates motor torquefor traveling operation from the rotation position command Pref andcurrent rotational position θr to deliver the motor torque thus obtainedto an adder 54.

Moreover, when load torque T₁ is applied to the base 4, sensor signalsPS₁, PS₂, PS₃, PS₄ of the pressure sensors 15 are delivered to anadjuster 55. Thus, the adjuster 55 calculates the above-describedestimated load torque T₁′ on the basis of these sensor signals.

At the adder 54, motor torque Tgyr from the attitude controller 51 andmotor torque from the motor controller 53 are added. At a subtracter 56,estimated load torque T₁′ is subtracted from the added value mentionedabove. The torque thus obtained results in final motor torque Tm. Themotor torque Tm thus obtained is delivered to a motor rotor 57. At anadder 59, reactive force of the motor torque Tm and load torque T₁ areadded. The added value thus obtained is delivered to a motor stator/base60.

The motor rotor 57 is rotationally controlled in accordance with motortorque Tm. Rotational position θr of the motor rotor 57 is convertedinto 1/N by a deceleration 61 having deceleration ratio of N:1. Therotational position thus converted is transmitted to the wheel 3.Namely, rotational position θw of the wheels 3 is 1/N of the rotationalposition θr of the motor rotor 57. The rotary encoder 58 detectsrotational position θr of the motor rotor 57 to deliver a detectionsignal to the subtracter 52.

On the other hand, since added value of reactive force of the motortorque Tm and load torque T₁ is applied to the motor stator/base 60 in amanner as described above, but theses values are mutually canceled,inclining (tilting) operation of the motor stator/base 60 is suppressed.

FIG. 15 represents the processing in the block diagram shown in FIG. 14as mathematical model by using Laplace operator. As described above,deviation between base angle command θref and current base angle θ₀ isdelivered to the attitude controller 51, and deviation betweenrotational position command Pref of the motor rotor 57 and currentrotational position θr is delivered to the motor controller 53. At theattitude controller 51 and the motor controller 53, respective motortorques are calculated by feedback control which performs, e.g., PID(Proportional-plus-Integral-plus Derivative (Differential)) operation.Namely, Kp₀, Kp₁ become proportional gain, Ki₀, Ki₁ become integral gainand Kd₀, Kd₁ become derivative (differential) gain. By these controlgains, following characteristic in which the motor responds to attitudecommand θref and traveling command Pref is changed. For example, whenproportional gains Kp₀, Kp₁ are reduced, the motor rotor 57 would movewith slow following delay. When proportional gains Kp₀, Kp₁ areincreased, the motor rotor 57 would follow at high velocity. By changingthe control gain in this way, it becomes possible to adjust attitudecommand θref, traveling command Pref, and magnitude of error of actualmovement and/or response time.

Further, motor torque Tm in which estimated load torque T₁′ issubtracted from added value of motor torque from attitude controller 51and motor torque from the motor controller 53 is delivered to the motorrotor 57 so that the motor rotor 57 rotates by rotation angle θr. Here,Jr is inertia of the motor rotor 57, and Dr is viscosity resistance(damper factor) of the motor rotor 57.

On the other hand, while added value of reactive force of the motortorque Tm and load torque T₁ is applied to the motor/base 60 in a manneras described above, those torques are mutually canceled so thatinclinating operation is suppressed. Here, J is inertia of the motorstator/base 60, and D is viscosity resistance (damper factor) of themotor stator/base 60.

The mathematical model shown in FIG. 15 is as shown in FIG. 16, forexample, in more detail. As shown in FIG. 16, an attitude controller 70serves to perform PID control with respect to deviation between baseangle command θref and current base angle θ₀ to thereby generate motortorque Tgyr for attitude control. A motor controller 71 serves toperform PID control with respect to deviation between rotation positioncommand Pref and current rotation position θr of the motor 10 to therebygenerate motor torque for traveling control. Moreover, an adjuster 72serves to generate estimated load torque T₁′ from sensor signals of thepressure sensors 15. At an adder 73, these respective torques are added.The motor torque Tm thus obtained is delivered to the motor 10. Themotor 10 is rotationally driven by the motor torque Tm. Thus, itsrotation is converted into 1/16 by a decelerator 74 having decelerationratio of 16:1. The rotation thus converted is transmitted to the wheel3.

While explanation has been given above in FIGS. 12 to 16 on the premisethat single wheel 3 is provided for the brevity, e.g., attitudecontroller 51 in FIG. 14 is commonly used at left and right wheels 3R,3L, whereas motor controllers 53 are independently provided at left andright wheels in actual coaxial two-wheeled vehicle 1 having two left andright two wheels 3R, 3L.

The block diagram of the control mechanism in this case is shown in FIG.17. A sensor value ωp from the gyro sensor 13 is sent to an anglecalculator 82 through a Band-Pass Filter (BPF) 80 having passband of,e.g., 0.1 to 50 Hz, and a sensor value αp from the acceleration sensor14 is sent to an angle calculator 82 through a Low-Pass Filter (LPF) 81having cut-off frequency of, e.g., 0.1 Hz. At the angle calculator 82,current base angle θ₀ is calculated on the basis of these sensor values.Further, at a subtracter 83, deviation between base angle command θrefserving as attitude command and current base angle θ₀ is taken. Thedeviation thus obtained is delivered to an attitude controller 84. Theattitude controller 84 calculates the above-described motor torque Tgyrfrom the base angle command θref and current base angle θ₀.

On the other hand, at a subtracter 85R, deviation between rotationalposition command Rrefr of a motor rotor 92R serving as traveling commandfor right wheel 3R and current rotational position θr of a motor rotor92R detected by a rotary encoder 93R is taken. The deviation thusobtained is delivered to a position proportional controller 86R. Theposition proportional controller 86R performs positional proportion (P)control with respect to the deviation to deliver the proportion controlresult to a subtracter 87R. Further, a differentiator 88R differentiatesrotational position θr of the motor rotor 92R delivered from the rotaryencoder 93R to deliver differentiated result to the subtracter 87R.Further, at the subtracter 87R, deviation between proportional controlresult from the position proportional controller 86R and differentiatedresult from the differentiator 88R is taken. The deviation thus obtainedis delivered to a velocity proportional controller 89R. The velocityproportional controller 89R performs velocity proportion (P) controlwith respect to the deviation to deliver the proportional control resultto the adder 90. At the adder 90R, the proportional control result,motor torque Tgyr, and estimated load torque T₁′ determined from sensorsignals PS₁, PS₂, PS₃, PS₄ of the pressure sensors 15 at an adjuster 94are added. The added value thus obtained is delivered to a currentcontrol amplifier 91R. The current control amplifier 91R serves togenerate motor current on the basis of the added value to drive themotor rotor 92R. Rotational position of the motor rotor 92R is deliveredto the differentiator 88R along with the subtracter 85R. Since this issimilar also with respect to the left wheel 3L, explanation will beomitted.

As stated above, since the coaxial two-wheeled vehicle 1 in thisembodiment has control mechanism for attitude stabilization controlcommon to left and right wheels 3R, 3L and left and right independentcontrol mechanism for traveling control, and these control mechanismsperform independent control operations, it becomes possible to stablyand compatibly perform the attitude stabilization control and thetraveling control.

Then, the velocity control of the coaxial two-wheeled vehicle 1 in thisembodiment will be explained.

As described above, in the coaxial two-wheeled vehicle 1 in thisembodiment, gravity center coordinate (X_(g), Y_(g)) of load and itsload weight W_(g) on the base 4 are detected from sensor signals PS₁,PS₂, PS₃, PS₄ of four pressure sensors 15 ₁ to 15 ₄ provided at fourcorners of the base 4 to determine load torque T₁. In this case, thegravity center coordinate (X_(g), Y_(g)) is used as control command fortraveling direction and velocity.

In concrete terms, in the case where load weight W_(g) is apredetermined value or more, velocity command Vx is changed as shown inFIG. 18, for example, on the basis of X coordinate X_(g) of gravitycenter position. Here, in FIG. 18, the range from X₃ to X₁ is stopregion, and the command traveling velocity is caused to be zero withinthis range. It is preferable that the stop region is caused to beX-coordinate range of ground-contacting surface with respect to the roadsurface of the wheel 3. In this case, when, e.g., load weight W_(g) islarge, or gas pressure of the wheel 3 is low, since ground-contactingsurface with respect to the road surface of the wheel 3 becomes large,the range of the stop region also becomes large. By providing the stopregion (dead band) in this way, it can be prevented that the vehiclebody advances or reverses (withdraws) by slight gravity center movementthat the rider does not intend.

When X-coordinate is X₁ or more, command velocity is increased inaccordance with magnitude of the X-coordinate until vehicle velocityreaches the advancing maximum velocity S fMAX. Moreover, when theX-coordinate becomes equal to X₂ or more, deceleration/stop operation iscompulsorily performed. Thus, the vehicle body moves until the attitudeis stabilized within the stop region for a second time, and is thenstopped. By providing the region where deceleration/stop operation iscompulsorily performed, it is possible to maintain safety of rider whentraveling operation is performed at the maximum velocity. Similarly,when the X-coordinate becomes equal to X₃ or less, command velocity isincreased in accordance with the magnitude of the X-coordinate untilvehicle velocity reaches reversal (withdrawal) maximum velocity S bMAX.It is to be noted that it is preferable that the reversing maximumvelocity S bMAX is smaller than the advance maximum velocity S fMAX. Inaddition, when the X-coordinate becomes equal to X₄ or less,deceleration/stop operation is performed. The vehicle body moves untilthe attitude is stabilized within the stop region for a second time, andis then stopped.

Within the range where the X-axis coordinate is from X₁ to X₂, or fromX₃ to X₄, the rotational position command Prefr of the monitor 10R andthe rotional position command Prefl of the motor 10L are generated bythe following formula (19), for example, in accordance with theX-coordinate X_(g). Here, in the formula (19), G₀ is positive constantgain, and is permitted to be adjustable in accordance with, e.g., loadweight W_(g).Prefr=Prefl=X _(g) *G ₀  (19)

It is to be noted that it is preferable to perform traveling operationthat in the case where velocity command at time t=0 is Vx₀ and velocitycommand at time t=t₁ is Vx₁, acceleration is continuously changed sothat mechanical resonant oscillation does not take place. In this case,when the time until time reaches Vx₁ is assumed to be Δt, travelingvelocity command Vref(t) at time t (0≦t≦t₁) can be calculated by thefollowing formula (20), for example.Vref(t)=(¼)t ⁴−(⅔)Δt*t ³+(½)Δt ² *t ² +Vx ₀  (20)

At this time, rotational position command Pref(t) of the motor 10results in value obtained by integrating traveling velocity commandVref(t) of the formula (20), and is given by the fifth-order function asindicated by the following formula (21). Here, in the formula (21),Pref₀ is rotational position command at time t=0.

$\begin{matrix}\begin{matrix}{{{Pref}(t)} = {{\int{{{Vref}(t)}{\mathbb{d}t}}} + {Pref}_{0}}} \\{= {{\left( {1/20} \right)t^{5}} - {\left( {2/12} \right)\Delta\; t*t^{4}} + {\left( {1/6} \right)\Delta\; t^{2}*t^{3}} + {P\;{ref}_{0}}}}\end{matrix} & (21)\end{matrix}$

Moreover, in the case where not only forwarding/reversing operation isperformed, but also load weight W_(g) is a predetermined value or more,it is also possible to vary swivel velocity command Vr as shown in FIG.19, for example, on the basis of Y-coordinate Y_(g) of gravity centerposition. Here, in FIG. 19, the range from −Y₁ to Y₁ is stop region, andcommand swivel velocity is caused to be zero within this range. It is tobe noted that the stop region can be arbitrarily set in the vicinity ofthe origin O. By providing stop region (dead zone) in this way, it canbe prevented that the vehicle body swivels by slight gravity centermovement that the rider does not intend. When the Y-coordinate is Y₁ ormore, until vehicle velocity reaches clockwise maximum velocity C WMAX,command swivel velocity is increased in accordance with the magnitude ofthe Y-coordinate. Similarly, when the Y-coordinate reaches −Y₁ or less,until vehicle velocity reaches counterclockwise maximum velocity CCWMAX, command swivel velocity is increased in accordance with themagnitude of the Y-coordinate.

When the Y-coordinate is Y₁ or more, or is −Y₁ or less, rotationposition command Rrefr of the motor 10R and the rotation positioncommand Rrefl of the motor 10L are generated in accordance with the Ycoordinate Y_(g). In the case where traveling velocity is zero,rotational position command Rrefr of the motor 10R and rotationalposition command R refl of the motor 10L result in anti-phase command asindicated by the following formula (22), for example. Here, in theformula (22), G₁ is positive constant gain, and is permitted to beadjustable in accordance with load weight W_(g), for example.Rrefr=−Rrefl=Y _(g) *G ₁  (22)

On the other hand, in the case where traveling velocity is not zero,rotational position command Rrefr of the motor 10R and rotationalposition command Rref l of the motor 10L result in in-phase command asindicated by the following formulas (23), (24), for example. Here, inthe formulas (23), (24), G₂ is positive constant gain, and is permittedto be adjustable in accordance with load weight W_(g), for example.Rrefr=Prefr+Y _(g) *G ₂  (23)Rrefl=Prefl−Y _(g) *G ₂  (24)

Here, in the case where the vehicle body travels on a road surfacehaving uneven portions such as irregular road surface, etc., or inclinedroad surface, the vehicle body becomes difficult to travel in a targetdirection given by rotational position command for the left and rightmotors 10R, 10L so that there is the possibility that deviation may takeplace between target direction and actual traveling direction. Moreover,also in the case where effective diameter of the wheel 3 may vary bydifference between gas pressures of left and right wheels 3R, 3L, thereis the possibility that deviation may similarly take place betweentarget direction and actual traveling direction. In view of the above,in the coaxial two-wheeled vehicle 1 in this embodiment, actualtraveling direction is detected by gyro sensor 13 which detects angularvelocity ωyaw about the yaw axis to independently control rotationvelocities of left and right motors 10R, 10L to thereby eliminatedeviation between the target direction and the actual travelingdirection.

As an example, explanation will be given in connection with the casewhere effective diameter of the left wheel 3L is shorter than that ofthe right wheel 3R, and ωyaw₁ [rad/sec] is detected as a gyro sensorsignal about the yaw axis in performing straight forwarding operation.In such a case, when additive average of rotational velocity commandsVrefr, Vrefl is assumed as Vref₀, and rotational velocity commandsVrefr, Vrefl given to the left and right motors 10R, 10L are correctedas shown in the following formulas (25), (26), thereby permitting thevehicle body to perform straight forwarding operation. Here, in theformulas (25), (26), K₀ is positive constant.Vrefr=Vref ₀ −K ₀*ω_(yaw1)  (25)Vrefl=Vref ₀ +K ₀*ω_(yaw1)  (26)

Moreover, in the case where Dref [rad/sec] is given as target direction,rotational velocity commands Vrefr, Vrefl are applied to left and rightwheels as shown in the following formulas (27), (28).Vrefr=Vref ₀ −K ₀(Dref−ω _(yaw1))  (27)Vrefl=Vref ₀ +K ₀(Dref−ω _(yaw1))  (28)

The rotation velocity commands Vrefr, Vrefl obtained in this way areconverted into rotation position commands Prefr, Prefl of the wheelsrespectively by the following formulas (29), (30). Here, in the aboveformulas (29), (30), k is integer indicating the number of samplingoperations, and Pref (k) indicates rotation position command at k-thsampling.Rrefr(k)=Prefr(k)+Vref ₀  (29)Rrefl(k)=Prefl(k)+Vref ₀  (30)

Similarly, also in the case where the vehicle body swivels, there is thepossibility that deviation may take place at swivel velocity resultingfrom difference between gas pressures of left and right wheels 3R, 3L,and/or difference of the road surface situation, etc. Also in this case,actual swivel velocity is detected by gyro sensor 13 which detectsangular velocity ωyaw about the yaw axis to independently controlrotation velocities of the left and right motors 10R, 10L, therebymaking it possible to eliminate deviation between target swivel velocityand actual swivel velocity.

As an example, explanation will be given in connection with the casewhere effective diameter of the left wheel 3L is shorter than that ofthe right wheel 3R, and ωyaw₂ [rad/sec] is detected as a gyro sensorsignal about the yaw axis in performing swivel operation. When signalsobtained by differentiating rotation position command Rrefr of the rightwheel 3R and rotation position command Rrefl of the left wheel 3L arerespectively Vrefr, Vrefl, error ωerr of the swivel velocity isrepresented by the following formula (31).ω_(err)=(Vrefl−Vrefr)−ω_(yaw2)  (31)

In this case, rotation position commands Rrefr, Rrefl given to left andright motors 10R, 10L are corrected as shown in the following formulas(32), (33), thereby making it possible to swivel the vehicle body in amanner suited to the target. Here, in the formulas (32), (33), G₃ ispositive constant gain, and is permitted to be adjustable in accordancewith, e.g., load weight W_(g).Rrefr=Prefr+Y _(g) *G ₂−ω_(err) *G ₃  (32)Rrefl=Prefl−Y _(g) *G ₂+ω_(err) *G ₃  (33)

As stated above, in the coaxial two-wheeled vehicle 1 in thisembodiment, actual traveling direction and actual swivel velocity aredetected by gyro sensor 13 which detects angular velocity ωyaw about theyaw axis to independently control rotational velocities of left andright motors 10R, 10L, thereby making it possible to eliminate deviationbetween target direction (swivel velocity) and traveling direction(swivel velocity).

Moreover, in the case where the vehicle body travels on a road surfacehaving offset, there is the possibility that impact force may be exertedon the vehicle body when the wheels 3 ride over the offset, or descenddown the offset so that rider falls down. In view of the above, in thecoaxial two-wheeled vehicle 1 in this embodiment, acceleration sensor 14which detects linear acceleration Az in the Z-axis direction is utilizedto reduce command traveling velocity in the case where accelerationchange in the Z-axis direction has taken place to thereby relax impactforce to the vehicle body.

As an example, explanation will be given in connection with the casewhere the vehicle body travels on a road surface having offset as shownin FIG. 21A. When the vehicle body rides on the offset at time t₁ whileit travels at traveling velocity Vx₀ as shown in FIG. 21B, accelerationAz in the Z-axis direction takes place. When absolute value |Az| of theacceleration Az becomes equal to threshold value A₀ or more, the vehiclebody begins to decelerate. Namely, when integer indicating the number oftimes of sampling operations is assumed to be k, and traveling velocityat the k-th sampling is assumed to be Vx(k), until traveling velocityreaches the minimum value which has been set on the basis of absolutevalue |Vx(k)| of traveling velocity Vx(k), the vehicle body isdecelerated in accordance with the following formula (34), for example.Here, in the formula (34), ka₀ is positive constant.v _(x)(k)=v _(x)(k−1)−K _(α0) *|A _(z)|  (34)

Moreover, when absolute value |Az| of acceleration Az is below thethreshold value A₀ after deceleration, until traveling velocity reachesthe maximum value which has been set on the basis of absolute value|Vx(k)| of traveling velocity Vx(k), the vehicle body accelerates inaccordance with the following formula (35), for example. Here, in theformula (35), ka₁ is positive constant.v _(x)(k)=v _(x)(k−1)+K _(α1)  (35)

As stated above, in the coaxial two-wheeled vehicle 1 in thisembodiment, in the case where acceleration sensor 14 which detectslinear acceleration Az in the Z-axis direction is utilized so thatacceleration change in the Z-axis direction takes place, e.g., in thecase where the vehicle body rides on an offset, traveling velocity Vx isreduced to thereby have ability to relax impact force to the vehiclebody. It is to be noted that gyro sensor 13 may be used in place of theacceleration sensor 14.

While the coaxial two-wheeled vehicle 1 can travel while performingattitude stabilization control as stated above, image recognition meansand sound (speech) recognition means which will be explained in a manneras described below are provided to thereby have ability to realize highlevel function.

For example, ordinarily, the rider determines traveling direction byvisual sense. However, since when traveling velocity is increased, eyeof the rider is directed farther, there is the possibility that theretakes place the problem that the road surface below the foot cannot beseen so that he falls down by uneven portion or offset of the roadsurface. Moreover, also in the case where the coaxial two-wheeledvehicle 1 is caused to independently travel, when uneven portions of theroad surface and/or obstacle on the road source cannot be detected,there is the possibility that there may take place the problem that thevehicle body collides with obstacle, and/or the problem that the vehiclebody becomes unstable so that it falls down.

In view of the above, in the coaxial two-wheeled vehicle 1 in thisembodiment, as shown in FIG. 22A, two CCD cameras 17 (17R and 17L) aremounted on the base 4 close to the road surface. Accordingly, by usingthese CCD cameras 17R, 17L, as shown in FIG. 22B, it is possible todetect road surface environment close thereto by tigonometrical surveymethod from difference between left and right images, e.g., obstacle OBor magnitude and position and/or uneven portion of the road surface ofobstacle OB. Thus, it becomes possible to avoid the road surfaceenvironment where the vehicle body cannot travel, or to avoid obstacleof the road surface in non-contact manner.

Moreover, it is also possible to specify object designated by imagerecognition, e.g., moving object like human being to perform travelingoperation of the vehicle body in a manner followed thereby.

Further, in the coaxial two-wheeled vehicle 1 in this embodiment, asshown in FIG. 23A, two microphones (18R and 18L) are mounted on the base4 close to the road surface. By using these two microphones 18R, 18L, itis possible to estimate direction and distance of sound source SD asshown in FIG. 23B. Thus, e.g., it becomes possible to respond to soundsource, or to rotate the wheels 3 so that the vehicle body is orientedtoward sound source direction. Further, in the case where the vehiclebody is near the sound source, it is possible to stop travelingoperation to thereby have ability to prevent collision against soundsource. Further, speaker recognition using audio signal is applied toregister in advance voice of user to turn ON LED or to produce sound(voice) in the case where that sound (voice) is recognized so thatvehicle body recognition in the case where it is stolen, and/orselection of vehicle body by voice of user when a large number of thesame kind of vehicle bodies are arranged can be made.

It is to be noted that since noise at the time of rotation of the wheel3, etc. is also inputted to the microphone 18 except for voice of thehuman being, there is the possibility that precise sound sourceestimation and/or speaker recognition may become difficult. In view ofthe above, in the coaxial two-wheeled vehicle 1 in this embodiment, inthe case where speech (sound) recognition or speaker recognition isperformed at the time of traveling operation, frequency component of anoise signal stored in the memory in advance is removed from an audiosignal on which noise is superimposed to perform sound sourceestimation, etc. on the basis of the audio signal from which noise hasbeen removed. Thus, also at the time of traveling operation, precisesound source estimation and/or speaker recognition, etc. can beperformed.

In concrete terms, as shown in FIG. 24, audio signals detected by leftand right microphones 18R, 18L are converted into digital signals atanalog/digital converters (ADC) 100R, 100L. The digital signals thusobtained are delivered to subtracters 101R, 101L. On the other hand,noise signals at various traveling velocities are stored in advance at anoise signal data base 102. When current traveling velocity signal isinputted to the noise signal data base 102, a noise signal correspondingto the traveling velocity is read out. The noise signal thus read out isdelivered to subtracters 101R, 101L. At the subtracter 101R, 101L,frequency component of the noise signal is removed from audio signalsdelivered from analog/digital converters 100R, 100L.

The speech (sound) recognition unit 103 not only determines positioncoordinate (Xs, Ys, Zs) of sound source by using audio signal from whichfrequency component of noise signal has been removed, but also specifiesspeaker who has speaked by using speaker data base 104 to deliver soundsource position coordinate (Xs, Ys, Zs) or speaker specifying signal toa target coordinate converting unit 105. The target coordinateconverting unit 105 allows, e.g., sound source position (Xs, Ys) in theX-Y coordinate system to be target position (Xref, Yref) to outputtraveling position command (Xref, Yref) and traveling velocity commandVref.

The software configuration of such coaxial two-wheeled vehicle 1 will beexplained by using FIG. 25. As shown in FIG. 25, the softwareconfiguration is caused to be realized as hierarchical structurecomprising, in order from hardware layer 150 of the lowest layer, kernellayer 151, on-body layer 152, network layer 153 and application layer154 of the uppermost layer.

The hardware layer 150 is a layer of circuit, wherein, e.g., motorcontrol circuit, central control circuit, and control circuit such assensor circuit, etc. are included. The kernel layer 151 is a layer forperforming various operations such as motor servo operation, attitudecontrol operation, traveling control operation and/or real timetraveling target value operation, etc. The layer 160 for the attitudetraveling control is constituted by the hardware layer 150 and thekernel layer 151.

The On-body layer 152 is a layer for performing speech recognition,image recognition, traveling target value operation, and/or generationof obstacle avoidance orbit, etc. The obstacle avoidance, followingtoward object and/or traveling toward sound source, etc. which have beendescribed in FIGS. 22A, 22B, FIGS. 23A, 23B are executed at this layer.Moreover, the network layer 153 located at the upper level includesnetwork communication interface, network communication for travelingcontrol information and/or image speech information, traveling planmanagement of the vehicle body, man-machine interface to and from rider,and/or three-dimensional image recognition data base management, etc.Further, the uppermost application layer 154 is a layer for performingremote traveling control by the network communication and/or dialogbetween rider and the vehicle body, etc. A hierarchy 161 for upper levelcontrol is constituted by the ON-body layer 152, the network layer 153and the application layer 154.

These respective layers are executed at sampling control periodsdifferent from each other, and the period thereof becomes longeraccording as corresponding layer proceeds to the upper layer. Forexample, at the hardware layer 150 of the lowest layer, its controlperiod is short period of 0.1 msec, whereas the control period is 1 msecat the kernel layer 151, the control period is 10 msec at the on-bodylayer 152, the control period is 100 msec at the network layer 153, andthe control period is long period of 1 to 100 msec at the applicationlayer 154.

Subsequently, the entire configuration of the circuit in the coaxialtwo-wheeled vehicle will be explained. As shown in FIG. 26, sensorsignals PS₁, PS₂, PS₃, PS₄ from the pressure sensors 15 ₁ to 15 ₄ aredelivered. The sensor circuit 200 delivers, in combination, to thecontrol unit 16, sensor signals ωp, ωyaw from the gyro sensors fordetecting angular velocities about the pitch axis and the yaw axis andsensor signals Ax, Ay, Az, αp, αr, αyaw from acceleration sensors 14 fordetecting linear acceleration in X, Y, Z axis directions, and angularvelocities about the pitch axis, the roll axis and the yaw axis inaddition to the above-mentioned sensor signals. Moreover, the speechprocessing circuit 201 is supplied with audio signals from themicrophones 18R, 18L, and the image processing circuit 202 is suppliedwith image signals from the CCD cameras 17R, 17L. The speech processingcircuit 201 and the image processing circuit 202 deliver the audiosignal and image signal to the control unit 16.

The control unit 16 generates, on the basis of these sensor signals andthe audio/image signals, motor torque Tgyr and rotational positioncommand Pref of the motor rotor serving as traveling command in a manneras described above to deliver these values to left and right motordrivers 203R, 203L. The motor drivers 203R, 203L calculate, on the basisof the motor torque Tgyr and the rotation position command Pref, etc. ofthe motor rotor, optimum motor currents for driving, e.g., motors 10R,10L of 200 W to deliver them to the motors 10R, 10L. Rotationalpositions of the motors 10R, 10L are determined by rotary encoders 11R,11L, and are fed back to the motor drivers 203R, 203L.

A servo ON/power switch 204 is connected to the control unit 16 and thepower switch 205, and a signal from the power switch 205 is delivered toa power management circuit 206. The power management circuit 206 isconnected to a battery 207, and delivers control power of 24V to voiceprocessing circuit 201 and image processing circuit 202, and deliversmotor power to motor drivers 203R, 203L. Regenerative powers of motors10R, 10L are delivered to the power supply management circuit 206through motor drivers 203R, 203L, and the power supply managementcircuit 206 charges the battery 207 by using the regenerative power.

The detailed internal configuration of the entire configuration shown inFIG. 26 will be explained by using FIGS. 27A and 27B. As shown in FIGS.27A and 27B, sensor signals PS₁, PS₂, PS₃, PS₄ from the pressure sensors15, sensor signals ωp, ωyaw from the gyro sensor 13, and sensor signalsAx, Ay, Az, αp, αr, αyaw from the acceleration sensor 14 are deliveredto the sensor circuit 200. The sensor circuit 200 performs gainadjustment of sensor signals PS₁, PS₂, PS₃, PS₄ from the pressuresensors 15 by, e.g., pressure gain of 10 mv/N to further convert thosesignals into digital signals through Analog-Digital converter (notshown) thereafter to deliver the signals thus converted to gravitycenter computational (operation) unit 210 of the control unit 16.Moreover, the sensor circuit 200 performs gain adjustment of sensorsignals ωp, ωyaw from the gyro sensor 13 by attitude gain of, e.g., 1.6V/rad sec⁻¹, and performs gain adjustment of sensor signals Ax, Ay, Az,αp, αr, αyaw from the acceleration sensor 14 by attitude gain of, e.g.,1.6 V/rad sec⁻² to further convert them into digital signals throughanalog-digital converter (not shown) thereafter to deliver the digitalsignals thus obtained to signal pre-processing unit 211. The signalpreprocessing unit 211 performs pre-processing to implement digitalfilter to an inputted signal, or to calculate offset adjustment quantityor attitude position, i.e., base angle θ₀.

The gravity center computing unit 210 calculates, on the basis of sensorsignals PS₁, PS₂, PS₃, PS₄ from the pressure sensors 15, gravity centerposition coordinate (Xg, Yg) of load on the base 4 and its load weightWg as previously described to deliver information of the gravity centerposition coordinate (Xg, Xy) and load weight Wg to traveling commandcalculator 212, and delivers information of Y-coordinate Yg of gravitycenter position and load weight Wg to swivel command generator 215. Thetraveling command calculator 212 generates velocity command Vx on thebasis of gravity center position X-coordinate-traveling velocitycharacteristic as shown in FIG. 18, for example, and the rotationalvelocity command generator 213 performs the previously describedfifth-order function operation on the basis of the velocity command Vxto thereby generate rotation velocity command Vref(t). The rotationvelocity command generator 213 delivers rotational position commandPref(t) to the rotation position command generator 214, the swivelcommand generator 215, and the attitude command generator 216.

The swivel command generator 215 generates phase command in performingswivel operation, e.g., Yg*G₁ on the basis of Y-coordinate Yg and loadweight Wg of the gravity center position delivered from the gravitycomputing unit 210, rotation angular velocity ωyaw about the yaw axisdelivered from the signal pre-processing unit 211, and rotation velocitycommand Vref(t) delivered from the rotation velocity command generator213 to deliver the phase command thus generated to a rotation positioncommand generator 214. The rotation position command generator 214integrates rotation velocity command Vref(t) delivered from the rotationvelocity command generator 213 to generate rotation position commandPref(t) to deliver rotation position commands Prefr(t), Prefl(t) to leftand right motor drivers. In this instance, the rotation position commandgenerator 214 generates rotation position commands Prefr(t). Prefl(t) bytaking phase command from the swivel command generator 215 inconsideration.

Here, the sound (speech) processing circuit 201 delivers an audio signalfrom the microphone 18 to the sound (speech) recognition section 219 ofthe control unit 16. The sound (speech) recognition section 219 performsprocessing for estimating, e.g., sound source position coordinate and/orspeaker on the basis of the audio signal to generate a travelingposition command in which its sound source position is caused to betraveling target. Moreover, the image processing circuit 202 delivers animage signal from the CCD camera 17 to an obstacle avoidance section 220of the control unit 16. The obstacle avoidance section 220 detectsobstacle on the road surface on the basis of the image signal togenerate a traveling position command for avoiding that obstacle. Theabove-described rotation position command generator 214 may alsogenerate rotation position commands Prefr(t), Prefl(t) on the basis ofthe traveling position command from the sound (speech) recognition unit219 or the obstacle avoidance unit 220.

The attitude command generator 216 calculates base angle command θrefserving as attitude command which has been explained by using FIG. 13 onthe basis of the rotation velocity command Vref(t) which has beendelivered from the rotation velocity command generator 213 to deliverthe base angle command θref thus calculated to a subtracter 217. At thesubtracter 217, current base angle θ₀ which has been determined at thesignal pre-processing unit 211 is subtracted from the base angle commandθref. The deviation thereof is delivered to an attitude controller 218.The attitude controller 218 performs PID control on the basis of thedeviation to determine motor torque Tgyr. It is to be noted that, inperforming the PID control, PI gain may be changed in accordance withload weight Wg on the base 4. In concrete terms, it is preferable thatwhen load weight Wg becomes large, proportional gain is increased andintegral gain is reduced. The attitude control unit 218 delivers themotor torque Tgyr to left and right motor drivers 203R, 203L.

In the motor driver 203R for right wheel 3R, at a subtracter 230R,deviation between rotation position command Prefr serving as travelingcommand for motor 10R and current rotation position θr of the motor 10Rwhich has been detected by the rotary encoder 11R is taken. Thedeviation thus obtained is delivered to a position proportionalcontroller 231R. The position proportion controller 231R performsposition proportional (P) control with respect to the deviation todeliver proportional control result to a subtracter 232R. Moreover, adifferentiator 233R differentiates rotation position θr of the motor 10Rwhich has been delivered from the rotary encoder 11R to deliverdifferentiated result to the subtracter 232R. Further, at the subtracter232R, deviation between proportional control result from the positionalproportional controller 231R and differentiated result from thedifferentiator 233R is taken. The deviation thus obtained is deliveredto a velocity proportional·integralal controller 234R. The velocityproprtional·integral controller 234R performs velocityproportional·integral (PI) control with respect to the deviation thusobtained to deliver proportional·integral control result to an adder235R. At the adder 235R, the proportional·integral control result andmotor torque Tgyr are added. The added value thus obtained is deliveredto a current control amplifier 236R. The current control amplifier 236Rgenerates motor current on the basis of the added value to drive, e.g.,motor 10R of 200 W. The rotational position of the motor 10R isdelivered to the differentiator 233R along with the subtracter 230R.Since this similarly applied to the left wheel 3L, the explanationthereof will be omitted.

The power supply management circuit 206 is connected to, e.g., a battery207 of 24V, and serves to deliver control power of 24V, 1 A to thecontrol unit 16, and to respectively deliver motor powers to the motordrivers 203R, 203L. Regenerative powers of motors 10R, 10L are deliveredthrough motor drivers 203R, 203L to the power supply management circuit206. Thus, the power supply management circuit 206 charges the battery207 by the regenerative powers.

As explained above, in the coaxial two-wheeled vehicle 1 in thisembodiment, there are provided attitude controller common to left andright wheels 3R, 3L, which generates motor torque Tgyr for performingangular control of the base 4 by using the gyro-sensor 13 and theacceleration sensor 14 and motor torque T₁′ for canceling load torque byusing the pressure sensors 15, and left and right independent motorcontrollers which generate motor torque for performing traveling controlby using the pressure sensors 15 so that those controllers performindependent control operations. For this reason, it is possible tostably and compatibly perform attitude stabilization control andtraveling control.

Moreover, in the coaxial two-wheeled vehicle 1 in this embodiment,traveling control is performed in accordance with gravity centercoordinate of load on the base 4. In this case, since stop regions (deadzones) are provided within the X-coordinate range and the Y-coordinaterange of the ground-contacting surface with respect to the road surfaceof the wheel 3, it can be prevented that the vehicle body advances,reverses (withdraws) and/or swivels by slight gravity center movementthat the rider does not intend.

Further, in the coaxial two-wheeled vehicle 1 in this embodiment, actualtraveling direction and actual swivel velocity are detected by gyrosensor 13 which detects angular velocity ωyaw about the yaw axis toindependently control rotational velocities of left and right motors10R, 10L, thereby making it possible to eliminate deviation betweentarget direction (swivel velocity) and traveling direction (swivelvelocity).

Furthermore, in the coaxial two-wheeled vehicle 1 in this embodiment,acceleration sensor 14 which detects linear acceleration Az in theZ-axis direction is utilized, whereby in the case where accelerationchange in the Z-axis direction takes place, e.g., the vehicle body rideson offset, traveling velocity Vx is reduced, thereby making it possibleto relax impact force with respect to the vehicle body.

It is to be noted that while the present invention has been described inaccordance with certain preferred embodiments thereof illustrated in theaccompanying drawings and described in detail, it should be understoodby those ordinarily skilled in the art that the invention is not limitedto embodiments, but various modifications, alternative construction orequivalents can be implemented without departing from the scope andspirit of the present invention as set forth by appended claims.

For example, while explanation has been given in the above-describedembodiments on the premise that swivel velocity command Vr is changed onthe basis of Y-coordinate Y_(g) of gravity center position on the base4, the present invention is not limited to such implementation, but thehandle 5 may be caused to have steering characteristic. In this case,potentiometer may be included at the base 4 to use the rotational anglePM in place of Y-coordinate Y_(g) of the gravity center position. Alsoin this case, it is preferable to provide stop region (dead zone) in amanner previously described.

INDUSTRIAL APPLICABILITY

In accordance with the above-described present invention, there areproduced a first torque for canceling torque based on load on the basewhich has been detected by load detecting means comprised of, e.g.,plural pressure sensors, a second torque for maintaining the base sothat it has a predetermined angle in correspondence with angle aboutwheel axle of the base which has been detected by angle detecting meanscomprised of, e.g., gyro sensor and acceleration sensor, and a thirdtorque for performing traveling operation in accordance with position ofthe load to instruct pair of respective drive motors to performoperations corresponding to the first to third torques to drive a pairof wheels. For this reason, the vehicle body is stable with respect toload weight change, and attitude control and traveling control can bestably and compatibly performed.

Moreover, in the case where position of load on the base is within apredetermined stop region, e.g., the range in a direction perpendicularto the wheel axle is within the range in a direction perpendicular tothe wheel axle of ground-contacting region where the pair of wheels arein contact with the load surface, traveling command is not sent. In thecase where such position is not within the stop region, travelingcommand corresponding to that position is sent, thereby making itpossible to prevent the vehicle body from advancing/reversing by slightgravity center movement that rider does not intend.

In addition, in the case where position of load on the base is within apredetermined deceleration region, e.g., within the region in thevicinity of the boundary of load detectable range by the load detectingmeans, traveling command to perform deceleration/stop operation is sent.In the case where such position is not within the deceleration region,traveling command corresponding to that position is sent. Thus, even inthe case where gravity center position is greatly shifted, it ispossible to stabilize attitude for a second time. As a result, safety ismaintained.

1. A coaxial two-wheeled vehicle comprising: a pair of wheels, a wheelaxle installed or provided between the pair of wheels, a base supportedon the wheel axle so that it can be inclined thereon, a pair of drivemotors attached on the base and for driving the pair of respectivewheels, load detecting means provided on the base for detecting aposition and weight of a load on the base, and angle detecting meansprovided on the base for detecting an angle of the base about the wheelaxle of the base, and a control unit for sending an operation command tothe pair of drive motors, wherein the control unit comprises: a firstcontrol mechanism adapted to generate a first torque for cancelingtorque based on the load, and to generate a second torque formaintaining the base so that it has a predetermined angle incorrespondence with the angle about the wheel axle of the base, and asecond control mechanism independent of the first control mechanism,which is adapted to generate a third torque for performing a travelingoperation in accordance with the position of the load measured by theload detecting means, thus to instruct the pair of respective drivemotors to perform operations corresponding to the first to thirdtorques.
 2. The coaxial two-wheeled vehicle as set forth in claim 1,wherein the load detecting means comprises plural pressure sensors. 3.The coaxial two-wheeled vehicle as set forth in claim 2, wherein thebase is composed of a supporting table and a movable table, and theplural pressure sensors are provided to at least four corners of thesupporting table, and the movable table is mounted thereon.
 4. Thecoaxial two-wheeled vehicle as set forth in claim 1, wherein the angledetecting means comprises a gyro sensor and an acceleration sensor.
 5. Acoaxial two-wheeled vehicle comprising: a pair of wheels, a wheel axleinstalled or provided between the pair of wheels, a base supported onthe wheel axle so that it can be inclined thereon, a pair of drivemotors attached on the base and for driving the pair of respectivewheels, load detecting means provided on the base for detecting aposition and weight of a load on the base, and angle detecting meansprovided on the base for detecting an angle of the base about the wheelaxle of the base, and a control unit for sending an operation command tothe pair of drive motors, wherein the control unit comprises: a firstcontrol mechanism adapted to generate a first torque for cancelingtorque based on the load, and to generate a second torque formaintaining the base so that it has a predetermined angle incorrespondence with the angle about the wheel axle of the base, a secondcontrol mechanism independent of the first control mechanism, which isadapted to generate a third torque for performing a traveling operationin accordance with the position of the load, thus to instruct the pairof respective drive motors to perform operations corresponding to thefirst to third torques, wherein swivel detecting means for detecting anangle about a vertical axis is provided on the base, and the controlunit serves to generate the third torque in accordance with position ofthe load and angle about the vertical axis.
 6. A coaxial two-wheeledvehicle comprising: a pair of wheels, a wheel axle installed or providedbetween the pair of wheels, a base supported on the wheel axle so thatit can be inclined thereon, a pair of drive motors attached on the baseand for driving the pair of respective wheels, load detecting meansprovided on the base for detecting a position and weight of a load onthe base, and angle detecting means provided on the base for detectingan angle of the base about the wheel axle of the base, and a controlunit for sending an operation command to the pair of drive motors,wherein the control unit comprises: a first control mechanism adapted togenerate a first torque for canceling torque based on the load, and togenerate a second torque for maintaining the base so that it has apredetermined angle in correspondence with the angle about the wheelaxle of the base, a second control mechanism independent of the firstcontrol mechanism, which is adapted to generate a third torque forperforming a traveling operation in accordance with the position of theload, thus to instruct the pair of respective drive motors to performoperations corresponding to the first to third torques, wherein theweight center of the base is located below the wheel axle.
 7. A coaxialtwo-wheeled vehicle comprising: a pair of wheels, a wheel axle installedor provided between the pair of wheels, a base supported on the wheelaxle so that it can be inclined thereon, a pair of drive motors fordriving the pair of respective wheels, means for generating a torque tothe drive motors for maintaining the base so that it has a predeterminedangle in correspondence with the angle about the wheel axle of the base,load detecting means provided on the base for detecting a position andweight of a load on the base in at least a direction perpendicular tothe wheel axle, and a control unit for sending an operation command tothe pair of drive motors, wherein the control unit is operative so thatin the case where the position of the load is within a predeterminedstop region having a certain non-zero width in said direction sufficientto comprise a dead band, it does not send a traveling command, while inthe case where the position of the load is not within the stop region,it sends a traveling command corresponding to that position to the pairof respective drive motors.
 8. The coaxial two-wheeled vehicle as setforth in claim 7, wherein the range in a direction perpendicular to thewheel axle of the stop region is within the range in a directionperpendicular to the wheel axle of a ground-contacting region where thepair of wheels are in contact with the road surface.
 9. A coaxialtwo-wheeled vehicle comprising: a pair of wheels, a wheel axle installedor provided between the pair of wheels, a base supported on the wheelaxle so that it can be inclined thereon, a pair of drive motors fordriving the pair of respective wheels, load detecting means provided onthe base for detecting a position and weight of a load on the base, anda control unit for sending an operation command to the pair of drivemotors, wherein the control unit is operative so that in the case wherethe position of the load is within a predetermined stop region, it doesnot send a traveling command, while in the case where the position ofthe load is not within the stop region, it sends a traveling commandcorresponding to that position to the pair of respective drive motors,wherein image pick-up means for picking up a forward image, and imageprocessing means for processing the image which has been picked up arefurther provided on the base, and the control unit sends a travelingcommand corresponding to processing result of the image processing meansto the pair of drive motors.
 10. The coaxial two-wheeled vehicle as setforth in claim 9, wherein the image processing means performs processingfor detecting position and distance of an obstacle from the image whichhas been picked up, and the control unit sends a traveling command foravoiding the obstacle to the pair of respective drive motors.
 11. Thecoaxial two-wheeled vehicle as set forth in claim 9, wherein the imageprocessing means performs processing for detecting position and distanceof a predetermined object from the image which has been picked up, andthe control unit sends a traveling command following the object to thepair of respective drive motors.
 12. A coaxial two-wheeled vehiclecomprising: a pair of wheels, a wheel axle installed or provided betweenthe pair of wheels, a base supported on the wheel axle so that it can beinclined thereon, a pair of drive motors for driving the pair ofrespective wheels, load detecting means provided on the base fordetecting a position and weight of a load on the base, and a controlunit for sending an operation command to the pair of drive motors,wherein the control unit is operative so that in the case where theposition of the load is within a predetermined stop region, it does notsend a traveling command, while in the case where the position of theload is not within the stop region, it sends a traveling commandcorresponding to that position to the pair of respective drive motors,wherein sound collecting means for collecting sound (speech)therearound, and speech (sound) processing means for processing thesound (speech) thus collected are further provided on the base, and thecontrol unit sends a traveling command corresponding to processingresult of the speech (sound) processing means to the pair of respectivedrive motors.
 13. The coaxial two-wheeled vehicle as set forth in claim12, wherein the speech (sound) processing means performs processing fordetecting sound source position of the sound (speech) thus collected,and the control unit sends a traveling command for following or avoidingthe sound source to the pair of respective drive motors.
 14. The coaxialtwo-wheeled vehicle as set forth in claim 12, wherein the speech (sound)processing means includes memory means in which noise signalscorresponding to traveling velocities are recorded in advance to removefrequency component of a noise signal corresponding to a travelingvelocity at the time of sound collection from the sound which has beencollected thereafter to perform speech (sound) processing.
 15. A coaxialtwo-wheeled vehicle comprising: a pair of wheels, a wheel axle installedor provided between the pair of wheels, a base supported on the wheelaxle so that it can be inclined thereon, a pair of drive motors attachedon the base and for driving the pair of respective wheels, means forgenerating a torque to the drive motors for maintaining the base so thatit has a predetermined angle in correspondence with the angle about thewheel axle of the base, load detecting means for detecting a positionand weight of a load on the base provided on the base in at least adirection perpendicular to the wheel axle, a control unit for sending anoperation command to the pair of drive motors, wherein the control unitis operative so that in the case where the position of the load iswithin a predetermined deceleration region having a certain non-zerowidth in said direction sufficient to comprise a dead band, it sends atraveling command for performing a deceleration/stop operation to thepair of respective drive motors, while in the case where the position ofthe load is not within the deceleration region, it sends a travelingcommand corresponding to that position to the pair of respective drivemotors.
 16. The coaxial two-wheeled vehicle as set forth in claim 15,wherein the deceleration region is a region in the vicinity of theboundary of a load detectable range by the load detecting means.
 17. Thecoaxial two-wheeled vehicle as set forth in claim 1, further comprisingan adder that adds the first and second torques, thus to instruct thepair of respective drive motors to perform operations corresponding tothe first to third torques.
 18. The coaxial two-wheeled vehicle as setforth in claim 7, wherein angle detecting means for detecting angleabout the wheel axle of the base is further provided on the base, andthe control unit is composed of a first control mechanism adapted togenerate a first torque for canceling torque based on the load, and togenerate a second torque for maintaining the base so that it has apredetermined angle in correspondence with the angle about the wheelaxle of the base, and a second control mechanism independent of thefirst control mechanism, which is adapted to generate a third torque forperforming a traveling operation in accordance with the position of theload, thus to instruct the pair of respective drive motors to performoperations corresponding to the first to third torques.
 19. The coaxialtwo-wheeled vehicle as set forth in claim 18, wherein the load detectingmeans comprises plural pressure sensors.
 20. The coaxial two-wheeledvehicle as set forth in claim 19, wherein the base is composed of asupporting table, and a movable table, and the plural pressure sensorsare provided at four corners of at least the supporting table, and themovable table is mounted thereon.
 21. The coaxial two-wheeled vehicle asset forth in claim 18, wherein the angle detecting means comprises agyro sensor and an acceleration sensor.